The present invention relates to lock-up clutch controls and more particularly to control valve assemblies for effecting automatic engagement of the lock-up clutch.
In an automatic transmission having a torque converter with a lock-up clutch, it is desirable to engage the lock-up clutch in each of the high forward speed ratios, such as a second speed ratio upward, for greater operating efficiency of the automatic transmission. However, a great shift shock takes place if a shift is effected with the lock-up clutch kept engaged. In order to eliminate the occurrence of the shifting shock, electronic controls have been proposed which release the engagement of the lock-up clutch temporarily during a shift between two speed ratios in the transmission. However, such electronic controls require expensive hardware including an electronic control unit, sensors and actuators.